+1 Think used. In 300 plus bikes in the last several years, I have yet to have bought a single new wheel, despite replacing probably at least 100 during that time. There may be a time where I buy a new wheel, but given my current inventory of spare wheels, it won't be anytime soon. I typically find them either on Craigs List (someone upgrading), garage sale, or in the form of a complete donor bike.

Another advantage of used wheels is they typically come complete with skewers, cassette, rim strips, even tires and tubes. Often, the value of the extras exceed the entire cost of the wheels.

+1 To Robbie below: sometimes the tires on used wheels are great, sometimes they are decent (usable for a flip), sometimes they are crap. But the tubes are almost always good.

You can even go the proactive route, place a WTB wheels in your local C/L, in the bikes for sale section (the wanted section gets ignored around here).